I tried the emerge $(qlist -I -C x11-drivers/) option with no joy. It fails the same way.

I noticed that Xorg.0.log has a comment about kbd and mouse being disabled, and I wonder whether anything is enabling these drivers. There are also error messages about dri and dri2 being missing. I do not specify these and I don't know where these came from. Perhaps one of these is the clue...

or simply leave out the sections. As far as I can see there's nothing in them that xorg needs. I'm not shure if leaving them out might make the ServerLayout section confuse xorg, but I get by with an almost empty xorg.conf. Only thing left is

Have you tried to downgrade back to xorg 1.13? The 1.14 ABI has only been supported since nvidia driver 313.18 (non-legacy; 304.84 otherwise), and there may be bugs. 313.26 works fine here with xorg 1.13.1.

(watch to get the proper names for your mouse and keyboard
as per their InputDevice sections)_________________.... there is nothing - absolutely nothing - half so much worth
doing as simply messing about with Linux ...
(apologies to Kenneth Graeme)

I am now starting acpid when I boot up and the error message is gone. nvidia starts up and hangs as before. I also tried nouveau and it fails because KMS is not enabled in my 3.7.10 system even though I've tried to do what the examples said would work. Sad that something that is absolutely required by an important driver isn't set by them, and worse that there is no option that forces KMS directly.

I agree that udev is probably my problem. Either udev isn't detecting the keyboard and mouse or it is creating devices that xorg isn't expecting. I need to study the link you gave me again, though.

Identifier can, to my knowledge, be what you wish. Coolbits is also optional, just for me to get some more functions up on nvidia-settings. Essentially, I think all you need is an identifier (never tried without, though), and the driver specified.

For nouveau you don't need even this, as far as I remember right. If you wanted to easily switch between the drivers, you would need different kinds of Kernel settings for nouveau to work, and you would need to blacklist the driver to be able to use nvidia instead... again, if I remember right. I never did that, but I'm pretty sure that's about the lines that goes~

I can't spot where or why this started happening to you, but this is what I use, and would suggest you to at least try and see what happens. Additionally, I'd check dmesg in case there is something of interest there.

Also, did you rebuild x11-drivers/xf86-input-evdev after downgrading xorg-server? For reference, I'm using x11-base/xorg-server-1.14.0(0/1.14.0) here, with nvidia-drivers-313.26.

Just some thoughts~
Good luck!_________________Kind Regards,
~ The Noob Unlimited ~

Here's what I did:
1. Figured out why acpid wasn't working and fixed that. No change.
2. Read the documentation on udev and made a few changes that it required. No change.
3. Went through the documentation on udev and made sure that the udev USE variable was set systemwide. No change.
4. Used udevadm to verify that udev was creating printer and mouse devices. It is.

5. Moved around the USE variables in /etc/portage/package.use so that udev wasn't last in the list of USE variables.
6. Decided to chase down the AutoAddDevice option in X. Tried setting the option to "true", because the documentation says to set it "false" to turn off auto detection. X wouldn't start at all, but I got an error message.
7. Tried Teegrins' minimal xorg.conf. It worked!
8. Commented the AutoAddDevice option out of my Nvidia xorg.conf file. It worked!

I find this very unsatisfying because I'm not sure what was wrong with having the USE variable at the end of the list. On the other hand, I am running Gentoo again and I am very happy.

Thanks to everybody for your advice and suggestions. It surely helps to have people interested in what you're doing.